Gas turbine engines are typically employed to power aircraft. Typically a gas turbine engine will comprise an axial fan driven by an engine core. The engine core is generally made up of one or more turbines which drive respective compressors via coaxial shafts. The fan is usually driven directly off an additional lower pressure turbine in the engine core.
A fan of the gas turbine engine generally includes a plurality of blades mounted to a hub. A fan casing and liner circumscribe the fan blades. Fan blades may be metallic or have a composite construction. Generally a composite fan blade will have a composite non-metallic core, e.g. a core having fibres within a resin matrix. Typically a composite blade will have a metallic leading edge to prevent erosion and to protect the blade against impact damage from foreign objects. The metallic leading edge generally wraps around the leading edge of the composite core and covers a portion of the suction surface of the blade and a portion of the pressure surface of the blade.
In the event of the leading edge becoming detached from the remainder of the fan blade (e.g. if a fan blade is released from the hub), the construction of the leading edge means that it can apply high impact forces to the fan casing. The fan casing and liner can be designed to absorb the impact energy imparted by a released blade and leading edge. However, this generally leads to a heavy system that has associated efficiency penalties.